1. Field of the Invention
This invention relates to a bearing unit for supporting the main shaft of high-speed rotating machine tools, and particularly to a bearing unit that is lubricated for example, with oil air and oil mist lubrication.
2. Description of the Related Art
Grease lubrication and oil lubrication are used mainly as the methods for lubricating bearings. In grease lubrication, lubrication is performed by filling the bearing with grease, and when compared with oil lubrication using lubrication oil that is supplied externally, it is generally possible to simplify the construction around the bearing to be lubricated as well as it is possible to better keep foreign matter from getting into the bearing from the outside. However, this method has a problem in that it is hard to cool the inside of the bearing, and to do with high-speed rotation.
In contrast to this, in the oil lubrication, relatively low-temperature lubrication oil is supplied from the outside to securely cool the bearing from the inside thereof so as to form an adequate lubricating oil film. In oil air and oil mist lubrication, which is one type of the oil lubrication, lubrication oil is fed to the inside of the bearing unit using compressed air, making it possible to perform lubrication more efficiently.
Oil air and oil mist lubrication is performed using a nozzle that ejects both air and lubrication oil. However, there is a problem in that the wind noise (Zxc2x7Fc component), which occurs due to the air that is ejected from the nozzle when rotation increases, becomes severe. Therefore, in oil air and oil mist lubrication, attempts have been made to reduce the noise by finely adjusting the position, shape and number of nozzles. However it is still not made quiet enough until now.
In consideration of this problem, it is an objective of this invention to provide a bearing unit that suppresses noise such as wind noise, and which is quieter.